Gliomas account for about 60% of all primary CNS tumors. Glioblastoma (GBM) or grade IV gliomas which comprise 50.9% of all gliomas are the most malignant form. Glioblastoma tumors are highly heterogeneous and there is a complex interaction among different types of tumor cells and stromal cells within the tumor. Recently it has been shown that the majority of tumor cells do not have the capacity to recapitulate a phenocopy of the original tumor and that only a small subpopulation of cells in the tumor, called cancer stem cells, have that ability upon xenotransplantation in nude mice. According to the cancer stem cell hypothesis, molecular alterations in cancer either convert normal stem cells into aberrant counterparts or cause a more differentiated cell to revert towards a stem cell-like behavior. These cancer stem cells appear to be more resistant to conventional therapy, as compared to the non-cancer stem cells. Following current therapy for high-grade glioma tumors, most patients die within a year from a new secondary tumor foci forming within one centimeter of the resected area. These foci are enriched for cancer stem cells, and it is likely that they are responsible for tumor recurrence. Targeted therapies aiming at eradication of glioma stem cells, or reverting these cells into a more differentiated state which can then responds to conventional therapy is highly beneficial and are current being tested in clinical trials using all-trans retinoc acids (ATRA; ://clinicaltrials.gov). In this proposal, we will optimize a triple secreted reporter system for high-throughput screening and use it to find modulators of glioma stem cells. We will simultaneously screen for drugs which either: (1) revert glioblastoma cancer stem cells into a more differentiated state, making them susceptible to conventional therapy; (2) eradicate these cells. Potential drug hits will then be analyzed in an intracranial glioma stem cells model which infiltrates the brain of mice similar to human tumors.